Wheel size revisited

Back in August I partici-raced the Red Clay Ramble down near Milledgeville, GA. It’s a great race and with a good course and excellent promotion.

I had a terrible race. Bike didn’t work, legs didn’t work, very tired and lowkey upset at my girlfriend so things just sucked.

My bike was a converted 26” hardtail running drop bars with 9 speed integrated shifters. Tires were 26×2.2 Forte Tasli which has a mild tread and weighs about 650 grams a tire.

I spent a good portion of the race yoyo-ing with the same dozen or so riders on cross bikes. What I noticed was that on gravel I would get gapped easily, any coasting down hill would see me off the back very quickly. Riding up the other side of a hill I would need to pedal sooner than my companions. I was redlined trying to stay in their draft.

Once we hit pavement I would easily catch and pass the other riders in my group.  

[Not to be rude but I’ve raced against these riders before and for the most part I have finished several dozen minutes ahead of them on other gravel courses like the Shake ‘n’ Brake, Mt Currahee and Southern Cross.]

Anyway, I recall Jan Hiene mentioned this phenomenon during his ride report for the Oregon Outback as well. He was on a randonneur-style road bike and was catching an MTB rider on the dirt sections but getting passed by the same rider on the pavement sections.

What I’ve been thinking about is the effect of wheel size. Everyone I was riding with was on a 700cx32/35/40 size wheel/tire combo. This combo is anywhere from 4-6% larger in circumference than my 26×2.2, could this have had an effect of slowing me down on the dirt?

Ok

So if the approach angle of a wheel is a determinant of rolling resistance, which we can sort of assume based on 26” to 29” experience in the MTB world, than a 26×2.2 is going to be at a disadvantage to bigger wheels when the road is rough.

Pavement is smooth, even on the roughest paved roads there are often only a few dozen roll-over obstacles in a given distance. The bumps you encounter are small and fast so you do not lose much to them regardless of tire size.

On a dirt or gravel road the roll-over obstacles are in the hundreds or thousands per mile. That’s part of why dirt speeds are so much slower than pavement speed no matter how smooth the dirt is. The rider is spending more time going up and down as opposed to forwards. Micro climbing all those rocks and undulations.

Here’s a picture I stole from REI’s website (EAT THE RICH)

attack_angle

And here’s a MTBR thread: http://forums.mtbr.com/general-discussion/29er-vs-650b-vs-26-%96-crude-analysis-701063.html

So I guess my point is I fucked up and should have made my 29er my gravel bike.

Shit.

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